We tested a series of amidine and related compounds against Trypanosoma brucei. The most active compound was a biphenyldiamidine that had an EC 50 of 7.7 nM against bloodstream-form parasites. There was little toxicity against two human cell lines with CC 50 > 100 μM. There was also good in vivo activity in a mouse model of infection with 100% survival at 3 mg/kg i.p. The most potent lead blocked replication of kinetoplast DNA (k-DNA), but not nuclear DNA, in the parasite. Some compounds also inhibited the enzyme farnesyl diphosphate synthase (FPPS), and some were uncouplers of oxidative phosphorylation. We developed a computational model for T. brucei cell growth inhibition (R (2) = 0.76) using DNA ΔT m values for inhibitor binding combined with T. brucei FPPS IC 50 values. Overall, the results suggest that it may be possible to develop multitarget drug leads against T. brucei that act by inhibiting both k-DNA replication and isoprenoid biosynthesis.
Keywords: computational modeling; farnesyl diphosphate synthase; kinetoplast DNA; proton motive force; sleeping sickness.